The present invention relates generally to seals for providing fluid sealing between a housing and a rotating shaft. More particularly, the invention relates to face seals in which a fluid is introduced between portions of the seal faces of the seal.
Conventional mechanical seals are employed in a wide variety of mechanical apparatuses to provide a pressure-tight and fluid-tight seal between a rotating shaft and a stationary housing. The seal is usually positioned about the rotating shaft, which is mounted in and protrudes from the stationary housing. The seal is typically bolted to the housing at the shaft exit, thus preventing loss of pressurized process fluid from the housing. Conventional split mechanical seals include face type mechanical seals, which include a pair of annular sealing rings that are concentrically disposed about the shaft, and axially spaced from each other. The sealing rings each have sealing faces that are biased into physical contact with each other. Usually, one seal ring remains stationary, while the other ring contacts the shaft and rotates therewith. The mechanical seal prevents leakage of the pressurized process fluid to the external environment by biasing the seal ring sealing faces into physical contact with each other. As a result of the repeated physical contact between the faces, abrasion of the seal faces occurs and the seals typically exhibit undesirable wear characteristics and leakage.
The poor wear characteristics of these conventional mechanical face seals necessitate the frequent monitoring and replacement of the seal components, particularly the seal rings. Replacement and repair of damaged seals have been facilitated by seal designs where a portion of the component parts of the mechanical seals are segmented or split. Installation of split or partially split seal components can be performed without necessitating the complete breakdown of the mechanical apparatus and without having to pass the annular seal over an end of the shaft. However, even in split seal designs, significant time is required to replace the seal components, resulting in frequent long periods of down time for the mechanical apparatuses associated with the seal.
The prior art attempted to overcome the above difficulties by employing non-contact mechanical seals that utilize a fluid interposed between the seal ring faces to reduce frictional wear. Conventional mechanical non-contact face seals typically employ spiral type-grooves formed in the hard face of the seal rings to develop a hydrodynamic lifting force that separates the seal faces. The resultant gap allows fluid to be disposed within the gap to prevent abrasion of the seal faces. These types of seals are limited in application because the seals are designed to operate in a unidirectional manner. If the seals are driven in the opposite direction, the seal rings typically do not separate but are pulled or sucked toward each other, thereby increasing wear and ultimately destroying the seals. Other conventional designs employ specially designed spiral grooves that can operate in both directions (bi-directional grooves). These grooves, however, are typically less efficient in separating the seal faces.
Even in mechanical non-contact seal designs a certain amount of seal face abrasion occurs, especially during start-up or during periods in which the shaft is rotating at relatively low speeds. Such abrasion causing wear of the seal components requires the eventual replacement of the seal components.
Few, if any, split-seal designs have been proposed for non-contacting seals. Difficulties have occurred in developing such a seal design due to the increased number of sealing surfaces in a split seal design and the presence of the fluid between the seal faces. The additional seal surfaces between each of the split segments of the seal components, and especially between the seal ring segments, make it difficult to maintain a fluid tight seal throughout the split seal. In addition, the fluid interposed between the seal faces can exert separation forces on the split seal components which can cause separation of the split components and further fluid leakage. For these reasons, there is a need in the art for a split, non-contact mechanical seal design that can provide a fluid-tight seal, while concomitantly providing the advantage of conventional split-seal designs.
As the above described and other prior art seals have proved less than optimal, an object of the present invention is to provide an improved split mechanical seal in which a fluid can be introduced between the seal faces while maintaining a relatively fluid-tight seal.
Another object of the invention is to provide a split mechanical seal operable under a wide range of operating conditions for a wide range of services.
Still another object of the present invention is to provide a split mechanical seal that is relatively easy to assemble or and to disassemble.
Yet another object of the invention is to provide a split mechanical seal that employs fluid at the seal faces to reduce wear while concomitantly preventing or minimizing leakage at the other faces, without compromising seal performance or integrity.
Other general and more specific objects of this invention will in part be obvious and will in part be evident from the drawings and the description which follow.
These and other objects are attained by the split mechanical face seal of the present invention in which each of the components of the seal can be split and a barrier fluid can be introduced to the seal faces of the stationary and rotary seal rings. The split mechanical seal of the present invention provides the advantages of a non-contacting seal design, e.g., reduced wear on the seal faces, as well as the advantages of split mechanical seal design, e.g. ease of installation and maintenance, while concomitantly preventing process fluid leakage across the seal surfaces. Additionally, the split mechanical seal of the present invention provides for adjustment of the degree of contact between portions of the seal faces and the flexibility and advantage of being suitable for gas or liquid barrier fluids applications, as well as for multiple environments.
The invention provides a split mechanical face seal that provides fluid sealing between a housing and a rotating shaft and includes first and second seal rings each having at least two seal ring segments and a radially extending seal face. The seal ring faces of the seal rings are opposed to one another. One of the seal rings is connected to and rotates with the rotating shaft, while the other seal ring is connected to the housing. The split mechanical seal also includes means for introducing a fluid to the seal faces of the first and second seal rings for establishing a seal therebetween and a split support member having at least two support segments for connecting the first seal ring to the housing or the rotating shaft.
The split support member can optionally include a split gland assembly having at least two gland segments that sealingly engage an outer surface of the first seal ring and connect the first seal ring to the housing. The split support member can also include at least one split resilient member, such as a split O-ring, interposed between the split gland assembly and the outer surface of the first seal ring for resiliently supporting the first seal ring in the radial direction.
The split seal can also optionally include a split holder assembly having at least two holder segments for connecting the second seal ring to the rotating shaft. At least one split resilient member, such as a split O-ring, can be interposed between the split holder assembly and the outer surface of the second seal ring. The split resilient member can resiliently support the second seal ring in the radial direction and the axial direction.
The split resilient member can also be positioned to permit pivoting of the second seal ring about the split resilient member to maintain co-planar alignment of the first seal face and the second seal face with respect to each other. In this manner coning of the seal faces, i.e., contact of the seal faces at either the outer or inner diameter of the seal rings due to pressure distortion of the seal rings, is controlled and the seal faces are maintained in a co-planar relationship.
The split seal can include a split shaft sealing member, such as a split O-ring, positioned between the rotating shaft and the split holder assembly. The split shaft sealing member provides a fluid seal between the shaft and the split holder assembly.
The means for introducing a barrier fluid can be a groove formed in the first seal face. The groove can be continuous about the first seal face and can be positioned to form two concentric seal faces on the first seal face thereby providing a dual seal. A continuous, circumferential groove can also be positioned on the first seal face to form lands on both sides of the circumferential groove. The barrier fluid can be a gas or a liquid or a combination thereof. In conjunction with other factors, such as the pressure of the barrier fluid, the groove can be dimensioned such that the barrier fluid within the groove provides a primarily hydrostatic force on the first and second seal faces to cause separation of at least a portion of the first seal face from at least a portion of the second seal face.
The means for introducing a barrier fluid to the first and second seal faces can include a fluid conduit formed through the first seal ring. The fluid conduit can have an opening at the first seal face and can extend substantially axially through the first seal ring to open at the outer surface of the first seal ring. A second fluid conduit can be formed in the split support member. The second fluid conduit can be positioned proximate to and in fluid communication with the fluid conduit formed in the first seal ring.
The split seal can optionally include a system for introducing a closing fluid to a rear surface of the first seal ring. The closing fluid exerts a closing force on the first seal ring that biases the first and second sealing faces towards one another into a sealing relationship. The system for introducing a closing fluid can be a fluid conduit formed in the split support member. The fluid conduit can have an opening proximate the rear surface of the first seal ring to facilitate the introduction of the closing fluid to the rear surface.
The split seal can also include a system for fluidly retaining the seal ring segments of the first seal ring in a sealing relationship in a negative pressure condition. The system for fluidly retaining the seal ring segments of the first seal ring in a sealing relationship can include a fluid conduit formed in the first seal ring for supplying barrier fluid to the outer surface of the first seal ring. The fluid conduit can have an opening in fluid communication with the means for introducing barrier fluid to the first and second seal faces.
The split support member can include a split holder assembly having at least two holder segments for radially supporting the first seal ring and connecting the first seal ring to the rotating shaft. The split seal can also include a gland assembly that sealing engages the outer surface of the second seal ring and connects the second seal ring to the housing.